1. Field of the Invention
The present invention relates to an arrester, such as a gas-filled discharge tube, for protecting an electric device from high-voltage surge which may be caused by lightning or the like. More particularly, the invention relates to the arrester's fail-safe mechanism which prevents the arrester from failing even if the arrester continues discharging for a long time and is therefore overheated as a result of long-time application of high-voltage surge.
2. Description of the Related Art
In general, an arrester is not overheated if its electric discharge occurs for a comparatively short time. However, if the discharge continues for a long time, the arrester may be overheated and fail. To prevent such an overheated condition, a conventionally-known arrester comprises a short-circuiting mechanism which short-circuits the discharge electrodes of the arrester in response to the overheated condition of the arrester, as is shown in FIGS. 1A and 1B. FIG. 1A is a partially-sectional view of the conventional arrester, and FIG. 1B is a plan view of the same.
Referring to FIGS. 1A and 1B, reference numeral 30 denotes a gas-filled arrester; 31, the main body of the arrester; 32, a ground electrode; 32', a terminal of the ground electrode; 33 and 33', line electrodes; 34 and 34', terminals of the line electrodes; 35, a metallic short-circuiting member; 36, a horizontal portion of the metallic short-circuiting member; 37, an engaging piece provided for the metallic short-circuiting member in a manner to engage with ground electrode 32; and 38 and 38', springy contact pieces which extend from the ends of horizontal portion 36 of metallic short-circuiting member 35 in such a manner that they can engage with line electrodes 33 and 33', with thermally-fusible, electrically-insulating spacers 39 and 39' interposed.
If arrester 31 shown in FIGS. 1A and 1B is overheated, insulating spacers 39 and 39' are thermally fused by heat. As a result, contact pieces 38 and 38' are pressed against line electrodes 33 and 33', due to their spring characteristics, thus short-circuiting line electrodes 33 and 33' to ground electrode 32. In this fashion, the occurrence of an accident arising from the overheated condition of the arrester is prevented.
The conventional arrester, such as that described above, is undesirably long. In addition, the metallic short-circuiting member of the arrester has a complicated construction. Therefore, the short-circuiting member cannot be fabricated without a waste of material, and the metallic mold for fabricating the short-circuiting member is costly.
Accordingly, an object of the present invention is to provide an arrester which is free from the above problems, is structurally simple and small-sized, and is easy to fabricate.